Most yo-yos are in the form of two disk-shaped side members that are rigidly connected to each other by a wooden or metal axle. One end of a string-type tether is secured to the yo-yo's axle. A second end of the tether includes a loop that is placed about one of the user's fingers to thereby secure the yo-yo to the user. When the tether is wound about the axle and the yo-yo is released from the user's hand, the yo-yo will begin to rapidly spin as the tether unwinds from the axle. Once the tether is fully unwound, the yo-yo may "sleep" at the end of the tether, whereby the yo-yo continues to spin without having the tether rewind on the axle.
Once the yo-yo is sleeping, there are a number of yo-yo tricks one can perform with the spinning yo-yo. In some of these tricks, the spinning yo-yo is temporarily placed upon a portion of the tether intermediate of the tether's two ends. At the end of most yo-yo tricks, the user will jerk his or her hand or in some other fashion cause the tether to go momentarily slack. This causes the tether to engage/snag the axle and/or the tether-facing surface of at least one of the yo-yo's side members. Once engagement has occurred, the end portion of the tether will move with the side member(s) and thereby wind about the axle. The winding of the tether on the axle causes the yo-yo to return to the user's hand.
There are three crucial performance characteristics of a yo-yo that enable a user to perform most of the well-known yo-yo tricks. The yo-yo must be capable of sleeping for an extended period of time, it must not be subject to inadvertent snagging on the tether, and it should return on command.
Concerning a yo-yo's sleep time, the longer the yo-yo can be made to sleep, the more time the user will have to complete any particular yo-yo trick. It is well known that by minimizing friction in the yo-yo, one can maximize the yo-yo's sleep time.
Concerning the ability of a yo-yo to not snag the tether, when a snag occurs, the yo-yo will automatically rewind on the tether. When this happens inadvertently, the trick being performed will often be ruined. Two major factors that influence whether a yo-yo will tend to accidentally snag on the tether are the size of the yo-yo's string gap (the area between the two side members in which the string/tether is located) and the configuration of the tether-facing surface of each side member. For tricks in which the yo-yo is placed on an intermediate portion of the tether, the string gap must be sufficiently wide to receive a second portion of the tether either atop or more preferably beside the permanently-secured portion of the tether. Once the additional tether portion is within the gap, there must still be sufficient clearance so that both tether portions do not inadvertently snag on either of the side members. However, too wide a string gap may preclude a user's ability to have the yo-yo return on command, since the wide gap may make it impossible for the tether to engage either side member.
Concerning the ability of a yo-yo to return on command, the structure and design of the yo-yo must be such that when the tether is slackened momentarily by the user, the tether can move slightly to thereby engage the axle and/or side members. Once engagement occurs, the tether should then wind tightly on the axle so that upon the yo-yo's next release from the user's hand, the unwinding of the tether will cause the maximum rotational speed of the yo-yo. The ease with which the tether engages/snags the spinning portions of the yo-yo is often facilitated through the use of particular adaptations in the tether-facing surface of each of the yo-yo's side members.
In the prior art, there have been a number of inventions designed to enhance one or more of the above-listed yo-yo characteristics. For example, both Kuhn et al (U.S. Pat. No. 5,100,361) and Isaacson (U.S. Pat. No. 3,175,326) teach low-friction yo-yos in which the axle includes ball bearings to enable an outer portion of the axle to remain stationary while an interior portion of the axle rotates with the yo-yo's side members. Because the end of the tether is secured to the outer portion of the axle, friction between the tether and the axle is virtually eliminated. This configuration also alleviates the problem in the prior art of rapid tether failure due to frictional heating and wearing of the portion of the tether that contacts a spinning portion of the axle. However, since the tether can only engage a side member to cause the yo-yo to return to the user, this makes it harder for the user to have the yo-yo return on command.
The yo-yo taught in the above-noted Kuhn patent includes structure that enables a user to adjust the width of the yo-yo's string gap. However, in the Kuhn yo-yo, as well as in all other prior art yo-yos, a compromise must be made between a wide string gap that would reduce the chance of inadvertent snagging of the tether and a narrow string gap that would increase the chance of said engagement when the user desires the yo-yo to rewind on the string. As a result, proper adjustment of the Kuhn yo-yo is difficult to achieve and maintain. In every prior art yo-yo, this compromise limits the performance of the yo-yo.
To make it easier for a user to have the yo-yo return on command, Amaral (U.S. Pat. No. 4,895,547) and others teach yo-yos in which the tether-facing surface of each side member includes a plurality of raised ribs that project toward the tether. The ribs are arrayed in a starburst pattern about the center axis of the yo-yo. When the yo-yo is spinning at the end of the tether and the tether is momentarily made slack by the user, the portion of the tether proximate the yo-yo's axle will engage one or more of the ribs to thereby cause the tether to move with the side member and thereby wind about the axle. It should be noted that since the ribs protrude from the side members, they effectively define the sides of the string gap and make the string gap dependent on the shape of the ribs. As a result, the non-uniform tether-facing surfaces can make it more difficult for a user to perform yo-yo tricks without having the tether inadvertently engage said ribs. In addition, premature tether breakage may occur due to frequent rubbing contact between the ribs and the tether. Furthermore, since the prior art ribs are taught as being angled relative to the substantially planar tether-facing surface of their associated side member, the ribs cause the string gap to vary in width dependent on the distance from the axle. This may cause the yo-yo to respond differently as the degree of twist in the tether changes. This occurs since the tether's twist affects the location of the beginning point of the tether's end loop (the portion of the tether that permanently encircles the axle), a location that is often the initial point of engagement between the tether and one or the other of the side members.
Chua, in GB patent 2132100, teaches another structure for facilitating a yo-yo's return. A rubber ring is inset into the tether-facing surface of each of the yo-yo's side members. The ring extends a full 360 degrees about the axle and functions to snag the tether when the tether contacts the ring's surface.